One example of an exhaust muffler is disclosed in Japanese Patent Laid-Open No. Hei 10-77822 (“JP '822”) wherein an upstream chamber and a downstream chamber that are held in fluid communication with each other are defined in a casing, and a conduit has a downstream end open into the upstream chamber and a pierced region including a plurality of fluid communication holes held in fluid communication with the downstream chamber that is joined to an exhaust pipe, whereby a flow channel in the casing is made variable by opening and closing the downstream end of the conduit with a valve.